Process and apparatus for the electrolytic decomposition of anhydrous magnesium chlorid and the production of magnesium or alloys thereof and chlorin



' E. A. ASHCROFT. PROCESS AND APPARATUS FOR THE ELECTROLYTIC DECOMPOSITION 0F ANHYDROUS MAGNESIUM cmomn AND THE PRODUCTION OF MAGNESIUM 0R ALLOYS THEREOF AND CHLORIN. APffLlCATlON FILED AUG-12 1919- 1,359,653. Patented Nov. 23, 1920.

3 SHEETS-SHEET 1. P E A74 i x ii E. A. ASHCROFT.

PROCESS AND APPARATUS FOR THE ELECTROLYTIC DECOMPOSITION OF ANHYDROUS MAGNESIUM CHLORIO AND THE PRODUCTION OF MAGNESIUM OR ALLOYS THEREOF AND CI'ILORIN,

jrrucmon man AUG-I2, 1919.

Pam maNOI 23, 1920.

3 MEETS-SHEET 2- 6K lua E. A. ASHCROFT. PROCESS AND APPARATUS FOR THE ELECTROLYTIC DECOMPOSITION 0F ANHYDROUS MAGNESIUM CHLORID AND THE PRODUCTION OF MABNESTUMOR ALLOYS THEREOF AND CHLORIN. APPLICATION FILED AUG-l2, 1919.

1,359,653.. Patented Nov.23, 1920.

3 8HEETSSHEET 3,

UNITED stares PATENT oFFicE.

EDGAR ARTHUR ASHCROFT, OF LONDON, ENGLAND.

PROCESS AND APPARATUS FOR THE ELECTROLYTIC DECOMPOSITION F ANHYDROUS MAGNESIUM CHLORID AND THE PRODUCTION OF MAGNESIUM OR ALLOYS THERE- OF AND CHLQRIN.

Specification of Letters Patent.

Patented Nov. 23, 1920,

Application filed August 12, 1919. Serial No. 317,083.

To all whom it may concern Be it known that I, EDGAR ARTHUR AsH- cnor'r, a subject of the King of Great Britain, residing at 65" London WVall, in the city of London, England, have invented new and useful improved processes and apparatus for the electrolytic decomposition of anhydrous magnesium chlorid and the production of magnesium or alloys thereof and chlorin, of which the following is a specification.

The principal object of my invention is to provide an eflicient process and apparatus whereby an electrolyte consisting of anhydrous magnesium chlorid alone, (or practically alone), can be resolved into its elements (magnesium metal and chlorin gas) and the magnesium metal can be obtained pure.

It is well known that the electrolytic production of the metal magnesium from magnesiumchlorid alone has never yet been possible in practice, and the general practice is to use, in the electrolytic cell, a double salt of magnesium and potassium, or the like, for instance carnallite, to which is often added calcium fiuorid, the extraneous salts constituting fluxes. It is furthermore (and in consequence of the presence of such fluxing salts) the general practice in existing processes to periodically dismantle the cell and gather the magnesium by allowing it to set in the electrolyte and afterward to break thesolidified electrolyte and separate the magnesium therefrom and purify it by refusion.

Such operations are exceedingly expensive and troublesome and moreover the presence of other metal salt in the electrolyte, according to the well known laws of mass reaction and electrolytic dissociation, unavoidably causes impurity to be deposited intothe magnesium while impurity is also gathered unavoidablv by the process of frequently dismantling the cell.

It has also been suggested to use such composite electrolytes and to receive the metal into some more electro-positive metal afterward recovering it therefrom by secondary electrolysis, the' electro-positive metals p ro posed for this purpose being copper alummiother.

that by none of these combinations can the pure metal be produced. The process according to my present invention can be carried out as follows.

I employ a twin cell electrolytic apparatus each cell being constructed preferably of cast steel and the respective cells being preferably alike in construction and design, but reversed in position relatively to each At the bottom of the said cell is a body of molten lead (preferably alloyed with about 5 to 10 per cent. of magnesium) the level being maintained constant by a weir extending across the cell and communicating with an outlet pocket, the other end of the cell communicating with an outlet pocket. The part of the cell which is exposed to the fused electrolyte is lined with refractory material such for instance as fireclay, or magnesia bricks, or tiles. The primary cell is fitted with a cover from which depend anodes, preferably of graphite, in electrical connection with the cover, but'insulated from the cell. The primary electrolyte is superimposed on the magnesium lead" alloy. The said electrolyte consists of fused anhydrous magnesium chlorid alone, or practically alone as far as the introduction of objectionable impurities. into the product is concerned. The electrolyte is consumed by the passage of the current and fresh quantities of crystalline anhydrous magnesium chlorid are added to maintain the electrolyte at the same level while the magnesium produced is received into the molten lead alloy.

In the secondary cell the reverse process takes-place. .An unconsumed and unchangeable body of electrolyte consisting also of magnesium chlorid alone, -or practically alone as aforesaid, is superimposed upon the alloy at the bottom of the cell. The cover of this cell is fitted with dependin cathodes,

consisting of iron, or steel, rods which dip into the secondary electrolyte and receive the deposit of magnesium, which floats in the said electrolyte. This cover is preferably fitted with separately removable sectional covers closing openings in the main cover so that access can be had to the cell for the removal of magnesium from time to dling, or otherwise transferring," the molten p1oyed; volts at the secondary cell, l to 2.5

alloy from pocket to pocket, at the respective ends of the adjacent twin cells.

The. process according to my invention is thus a continuous one and may be carried on with a minimum of labor and with great durability of apparatus. Anhydrous magnesium chlorid alone, or practically alone, is the only material employed and this 1s employed quantitatively in relation to the magnesium produced while the chlorin gas is also evolved quantitatively.- In the secondary cell the product of magnesium is also obtained quantitatively, and in a very high degree of purity.

To show the enormously improved working of the process according to my invention as against those hitherto employed I give the following data obtained from actual operation, but it is-to be understood that I do not limit myself to the details given.

Current eflicienc -90 to 95 per cent. VOltSg at the terminals 0 the primary cell, 4 to 6 volts according to the current density emvolts according to currentdensity employed. The current density employed may conveniently be such that the surplus energy evolved is sufiicient to maintain the contents of the vat in fusion. I have found the most suitable as follows :For an apparatus taking 5000 amperes I employ say twenty anodes, preferably of graphite, each about 3 inches in diameter and immersed about three inches in the electrolyte and one inch distant from the surface of the cathodic metal alloy while in the secondary cell I preferably em-. ploy four movable covers each of whichmay be fitted with say ,70 depending cathodes of 6 iron; or steel, each being about say threeeighthsof an inch in diameter and immersed half, an inch in the electrolyte and three quarters of an inch distant from the surface of the anodic metal alloy. Under these conditions. I obtain a terminal voltageof 6 volts for the primary cell and 2 volts for the secondary cell. I maintain the temperature of both cells at about 750 centrigrade which I have found gives the .best results.

. The anhydrous magnesium chlorid for the purposes of my invention may be obtained from ordinary crystalline hydrated magnesium chlorid of commerce-by subjecting it to any Suitable drying, or dehydrating, process, I prefer however to employ that decribed in thespecification of my application No. 317,082 for Letters Patent of even date herewith. The said anhydrous magnesium chlorid is fused and used alone (or practically alone) as the electrolyte.

I will now describe how my process may be performed and the appartus be constructed with reference to the accompanying drawings but I domotlimit myself to the precise details.

Figure l is a longitudinal section, Fig. 2 a plan, and F1g. 3 a transverse section of the apparatus, which comprises primary and' secondary cells (preferably made of cast steel) which, through their bodies are in electrical connection with each other as shown at w. The said cells may be of identical form, or construction, except in respect to the covers and electrodes as hereinafter described. Each of the said cells has a main part, or cell-proper, (marked respectively 1 and 2) 1n communication, by passages 4 and 5 at the bottom, with opposite pockets, 6 and 7, one pocket being for'introducing the alloy of magnesium and lead and the other being for withdrawing the alloy, the passage to the pocket 7 from the cell-proper being preceded, in the cell-proper, by a weir.8 extending across from side to side of thecell and rising to a. height the same "as that to which the alloy is required to rise, the'walls of the cell-proper rising to a greater height to hold the fused electrolyte and provide space for gaseous chlorin and to support the anodes 9, in the primary cell and the cathodes 10,in the F secondary cell, by, suitable insulated covers 11 and 12 which close the respective cells. The portion of the cell-proper 1 and Zabove the level of the top of the Weir S should be lined with fire-clay 13, or other suitable refractory, or protective, material and the undersides" of the covers be similarly rotected. The cells are arranged as a pair or in two, or more, pairs) side by side and close together in such relative positions that the alloy which iswithdrawn from the primary cell 1 can be conveniently trans- 'ferred to the secondary cell 2" and vice versa.

The primary cell 1, has'anodes 9, preferably of graphite, the alloy of lead and magnesium constituting the cathodes in this cell, while the secondary cell Zhas'cathodes 10 of iron, or

steel, the lead and magnesium alloy constituting the anode in this cell In this double cell arrangement the electric current passes through the two cells 1 and 2 in series, the anodes 9, in. the first cell 1, forming the positivepole and the iron, or steel, cathodes 10, inthe secondary cell2, forming the negative pole of the pair, while the molten alloy body forms a secondary, or intermediate, electrode. Any re; uired number of such pairs can be connects in series if desiredf J I prefer to mount the anodes 9 in openings in the cover 11 of the primaryv cell 1 and attach them by cementing or the like, electrical connection being secured by providing a number-of suitable conductors, 14, to the cover (which is in the electric circuit) of the cell which securing can be readily done by introducing the respective ends of the said conductors 14: into holes, in the cover, atone end and corresponding holes in the anodes 9 at the other end, molten lead being run in the holes to secure good electrical connection.

I prefer to carry the cathodes 10 in sets attached to any suitable number (say four) of supplementary covers 15, which are applied to openings in the main cover 12 which is in the electric circuit, each supplementary cover 15 being connected to the main cover 12 by a flexible conductor 16, so that any supplementary cover 15, with the set of cathodes 10 which it carries, can be instantly. removed by means of the handle 17 and be replaced without disturbing the rest of the apparatus.

In operating these cells a portion of the alloy, as it increases in volume by the addition of magnesium, passes over the weir 8 and into the pocket beyond, from which it is withdrawn and can be introduced into the secondary cell 2 through the adjacent pocket thereof. The alloy is passed, or caused to pass, periodically from cell to cell as hereinafter described, The electrolytic action of the current in the secondary cell causes the magnesium metal to collect at the iron, or steel, cathodes, the said metal floating on the electrolyte in molten condition. This magnesium metal, being uncontaminated by impurities, (which is an important advantage as against other processes for the production of magnesium), does not require re-fusion but may-be ladled from the cell and, for instance cast directly into any desired molds, or used directly in the extrusion process. I have found that no lead is deposited with the magnesium metal and that the pure, or practically pure, chlorid electrolyte prepared as aforesaid has no solvent action either on the magnesium deposited, or on the lead of the alloy so that a perfect, or almost perfect, current efiiciency is obtained. The conductivity is also extremely good.

In working the said cells the alloy should be allowed to remain tranquil, for a time, during the passage of the current, say for about six hours for each gatherin of the metal, thevoltage of the cell terminals remaining constant during this run because the slight shrinkage of the alloy in the secondary call is found to increase the resistance in the same proportion as the accumulation of the magnesium around the cathodes reduces the resistance. The magnesium metal floats in large masses in the fused electrolyte. When the magnesium metal has sufiiciently accumulated in the secondary cell the small covers and the cathodes thereof are successively removed, and the magnesium can then be readily ladled from the electrolyte and the cover and cathodes-be afterward replaced without the passage of the current having been interrupted, the whole operation occupying only a few minutes. From time to time, (preferably immediately after the gathering of the magnesium as hereinbefore explained), the alloy is passed briskly through the cells, from cell to cell, which can be done, for example, by ladling the alloy from the pocket of the primary cell and pouring it back into the pocket of the connected secondary cell, the pockets being conveniently arranged in reverse juxtaposition, as aforesaid, for the purpose. Or any convenient mechanical device, or arrangement of communicating passages, may be employed to effect the transference of the alloy. The openings 18 and 19 in the covers of the respective cells are for the introduction of the electrolyte.

What I claim is- 1. For use in the electrolytic decomposition of anhydrous magnesium chlorid and the production of magnesium metal and chlorin, a double electrolytic apparatus comprising two cells electrically connected in v series through their body-parts and each having pockets, passages at the bottoms of the cells establishing communication between said pockets, anda weir across each cell at a height approximately the same as that to which the alloy-body in each cell has to rise, the walls of each cell-proper rising to a greater height than the said alloy-body, and being adapted to contain the fused electrolyte and afford space for the gaseousproducts escaping during the decomposition of the electrolyte, covers for both cells, a high carbon anode supported in the Cover inthe primary cell, and an iron cathode supported in the cover in the secondary cell.

2. For use in the electrolytic decomposition of anhydrous magnesnim chlorid and the production ofmagnesium metal and chlorin, a double electrolytic apparatus of the construction specified in claim 1, a cover for the secondary cell having openings therein, supplementary covers applied to said openings, cathodes carried in sets attached to said supplementary covers, each of said supplementary covers being connected to the said main cover by a flexible conductor so that any one of the said supplementary covers, with the set of cathodes which it carries, can be removed and replaced without disturbing the rest of the apparatus or interrupting the electric current.

3. For use in the electrolytic decomposition of anhydrous magnesiumchlorid and name to this specification in the presence of i the production of magnesium metal and two subscribing Witnesses.

chlorin in the double cell arran 'ement specii 1 fied in claim 1, an electrolyte in both pri- EDGAR ARTHUR ASHCROFT 5 mary and secondary cells consisting substan- Witnesses:

tially solely of pure magnesium chloriol. G. F. LYoNs,

In testimony whereof I have signed my L. WALTER. 

